# Voltage divider doesn't work with ESP8266-01

Hi! I am trying to supply my ESP8266-01 from a 12V source. It is plugged into the wall and converts 220V AC to 12V DC. It has 0.2A. Because the ESP8266-01 doesn't support 12V, I have created a voltage divider with a 1.2kOhm and a 470Ohm resistor. I can measure about 3.5V with my multimeter (this is probably because the first resistor is not exactly 1.2kOhm, but 1.14kOhm), but the ESP8366 doesn't start. What could be the problem here? I will leave the schematic of the circuit below.

What could be the problem here?

You’re trying to use a voltage divider to do a voltage regulator’s job.

(Think about it: what is the effective resistance of the lower leg of the divider? (Hint: it isn’t 470R))

TheMemberFormerlyKnownAsAWOL:
You're trying to use a voltage divider to do a voltage regulator's job.

(Think about it: what is the effective resistance of the lower leg of the divider? (Hint: it isn't 470R))

So the problem is that the resistor takes too much current? (Sorry for the dumb question. I am new to electronics.)

You need to use a voltage regulator not a voltage divider. A voltage divider cannot be used for supplying power because:
1- It limits the current because of the resistors
2- The voltage it drops is dependent on the current through it. Basically your ESP acts like a variable resistor parallel to R2 which changes the resistor network and hence the output voltage.
A voltage divider is usually used when you want to "sense" a voltage, for example connecting it to an input pin of a microcontroller, where almost no current flow exists.

A voltage regulator on the other hand does exactly what you want. No matter what input voltage you give it, and no matter how much current goes through it, it will output a constant voltage. (There are limits however to how much current and input voltage you can give it)

There are many voltage regulator ICs available on the market. For example the famous lm317 adjustable regulator. And there are also voltage regulator modules available which make your life easier. I suggest you get a 3.3v "switching" voltage regulator module because your input voltage and current consumption are relatively high.
(A switching regulator is a regulator that is much more efficient and hence creates less heat. ESP uses about 80mA and your input voltage is 12V so (12-3.3)*0.080 = ~0.7Watts That's quite a lot of heat generated. If you use an ams1117 regulator it will probably die without a heatsink. An lm317 should be fine without a heatsink but still will get hot)

pourduino:
You need to use a voltage regulator not a voltage divider. A voltage divider cannot be used for supplying power because:
1- It limits the current because of the resistors
2- The voltage it drops is dependent on the current through it. Basically your ESP acts like a variable resistor parallel to R2 which changes the resistor network and hence the output voltage.
A voltage divider is usually used when you want to "sense" a voltage, for example connecting it to an input pin of a microcontroller, where almost no current flow exists.

A voltage regulator on the other hand does exactly what you want. No matter what input voltage you give it, and no matter how much current goes through it, it will output a constant voltage. (There are limits however to how much current and input voltage you can give it)

There are many voltage regulator ICs available on the market. For example the famous lm317 adjustable regulator. And there are also voltage regulator modules available which make your life easier. I suggest you get a 3.3v "switching" voltage regulator module because your input voltage and current consumption are relatively high.
(A switching regulator is a regulator that is much more efficient and hence creates less heat. ESP uses about 80mA and your input voltage is 12V so (12-3.3)*0.080 = ~0.7Watts That's quite a lot of heat generated. If you use an ams1117 regulator it will probably die without a heatsink. An lm317 should be fine without a heatsink but still will get hot)

Thank you!

Most circuits need a constant voltage supply, ie a voltage source (theoretically has zero output impedance,
so the voltage is fixed as the current varies).

In practice real voltage regulators are not that perfect, their output impedances are more like 0.1 ohm
or less, making them a good enough voltage source (500mA of current change produces <=50mV of voltage
change)

You could use a resistor divider to emulate this at the expense of extreme power wastage.

For instance you can divide 5V to 3.3V using a 0.15 and 0.3 ohm resistor, wasting 55W,
and get an output impedance of 0.1 ohms. However you need a 12A power supply minimum!

So in practical terms resistor dividers cannot be used as regulators.

The 1.2k resistor will limit the current provided by the 12V source to 10mA.
The esp needs 100mA or more.